3 0 0I unlocked this during Chapter 11.You can make progress towards this in a number of ways:1. Setting enemies on fire from barrel explosions, earliest method.2. Setting enemies on fire from sticky bomb explosions. Sticky bombs are an upgrade available for the crossbow.3. Once unlocked, the Flamethrower should help tremendously with unlocking this achievement.4. Once unlocked, setting enemies on fire from Rocket Launcher explosions should also count.Should unlock during initial playthrough. There may be a few other methods towards this, I will update if I find more or if comments are made.